A nonbonded potential field described by atom-atom (6-exp-1) functions has proved highly successful in the quantitative calculation of the crystal structures, heats of sublimation, thermal expansions, vibrational frequencies, elastic constants, bariers to molecular rotation, and lattice defects in hydrocarbons and hydrocarbon polymers. The same atom-atom nonbonded potentials also apply to interactions between different parts of the same molecule, e.g., to biopolymers such as proteins, nucleosides, and lipids. Recent developments indicate that coulombic interactions, previously neglected by most researchers, are highly significant even in hydrocarbons. These coulombic interactions will become even more significant in the force fields of molecules coulombic interactions merge toward chemical valence forces. A difficulty in the application of the atom-atom potential method has been the lack of availability of quantitative nonbonded potential parameters. Much more accurate hydrocarbon potentials have recently become available. The objective of this proposal is to extend the quantitative derivation of nonbonded potential parameters beyond simple hydrocarbon molecules to substances containg nitrogen, for model atom-atom potentials which will reproduce selected known intermolecular structures. The optimum parameters are those which most closely predict all the pertinent intermolecular properties of the basis experimental data. An important goal is to achieve force fields which will be transferable and therefore useful in dealing with new substances and with unknown intermolecular situations.